Has anyone seen the following error when running 'brew install clojure'? brew install clojure Error: No available formula with the name "clojure" Clojure isn't really a program but a library managed as part of a project and Leiningen is the user interface to that library. To install Clojure you should install Leiningen: brew install leiningen

you must be on a very old brew @jrbrodie77

I can brew install clojure just fine

@ghadi yes... turns out that reinstalling brew did the trick. brew update was also broken, which is how I ended up stuck on an older version. Didn't realize it would affect the package index.

Is it possible to define a custom implementation of toString for defrecords? I have already defined a clojure.core/print-method for the record-type in question, which helps in REPL, but is not useful when I try to generate formatted string with format functions. Looks like format function directly calls toString.

I'm using clojure.tools.deps.alpha to resolve-deps but I get:

Expanding javax.servlet/javax.servlet-api #:mvn{:version 3.1.0}
Execution error (ArtifactNotFoundException) at org.eclipse.aether.connector.basic.ArtifactTransportListener/transferFailed (ArtifactTransportListener.java:48).
Could not find artifact net.java:jvnet-parent:pom:3 in glassfish-repository ()

From last week. Any luck? It keeps biting me, especially after long sessions

I have had this problem too. Eventually I gave up on using tools.namespace refresh. I’m using the REPL more in the style of Stuart Halloway

Hi all does anybody know if a tool that would help to refactor function calls in a clj file that were created with a :refer :all to use a prefix?

For example I have a file with (:require [korma.core :refer :all]))... and within uses (update db-table (set-fields :myfield mydata) (where (:id id)))....

to be:

(:require [korma.core :as kdb])).... (kdb/update tb-table (kdb/set-fields :myfield mydata) (where {:id id})))... etc.

The compiler will tell you about undefined symbols if you just update your import statement

you can also use the joker linter, which will tell you even without compiling

it’s a killer feature when using this as an editor plugin

just removing and relying on the compiler might be a bit deceptive as there are some function names in the korma namespace that shadow clojure.core ones - for example update and so I am concerned that I may not get compiler errors in that case

ah good point

gunna try emacs / clj-refactor / stop-referring command

tools.deps question: when I depend on git dependency, is there a way to also specify an alias defined in that library to be used?

no

will there be such a way?

no

aliases are resolved first to determine what deps to traverse

but aren't they like a classifiers in poms?

no

kind of

> aliases are resolved first to determine what deps to traverse I meant to use alias defined in dependent library when specifying dependency, not using it in place where normal aliases are used

oh

haven’t thought about it

like that:

{:deps {git-dep/artifact {:git/url "..." :sha "..." :aliases ["blah"]}}}

this looks like classifier, and behaves kind of like classifier

(I mean expected to behave, not behaves)

I don’t think it’s like classifiers

classifiers select an alternate artifact

this is about selecting an alternate sub-classpath

right, this is more of a configure what bits to also include

well, feel free to file a TDEPS jira enhancement and I’ll think about it. not anything I’m going to do soon though.

Thanks, I will! I have a use case for it, but it's not very urgent and workarounds are possible while it's not there

hi, i’m trying to process a hierarchy and i think i have things working the way i like, but i can’t seem to figure out how to avoid an atom i want to get rid of… any tips appreciated. https://gist.github.com/joefromct/0b017d43f381e3f861fc93d08e716213 I think it’s trickier than just a recur with an accumulator because there is a couple of doseq’s in the middle there.

@alexmiller created https://dev.clojure.org/jira/browse/TDEPS-116

thx

Interestingly, TDEPS-116 could also open the way for a solution to managed dependencies. The lib/deps.edn is a file that describes managed deps via aliases. app/deps.edn consumes this lib and describes which managed deps (= alias in lib/deps.edn) it wants to include as deps.

I just did a (source promise) and discovered there's an undocumented behavior; a promise can act as a function equivalent to deliver on the promise. This is actually quite useful to me. Is this an intentional part of promise and, if so, should it be documented?

(def p (promise))
=> #'user/p
(p 37)
=> #object[clojure.core$promise$reify__8486 0x5742bdca {:status :ready, :val 37}]
@p
=> 37

I'll submit a patch to update the docstring if so.

@hlship for undocumented behavior you definitely shouldn't count on, I've seen deliver used to replace (fn [f x] (f x)) which relies on that behavior

the implementation seems to quite intentionally support that

(by implementing IFn)

So missing documentation: a bug, or leaving option open to remove this behavior?

I’d call it a doc bug

Ok, patch coming up!

can’t imagine we would remove it

I would make the patch small by just extending “… with deliver or by invoking the promise”

looking at it again, clearly deliver is the intended entry point so I think I’d call it an enhancement

Interesting; looking at the source for deliver, it is just (promise val). My thinking is that this usage in not intentional, it was just easier for Rich to re-use IFn than to define a new IDeliver interface. However, I think it is quite worth documenting and even using when appropriate.

hello all, Is there any exponentiation function of a double exponent? (function 4.554 <exponent_double>)

for both clj and cljs you can use Math/pow via interop

thansk

user=> (Math/pow 4.554 Math/E)
61.61660979210404

worked, many thnaks

You know, once you get over the parenthesis there is a lot of power to appreciate. I was about to write (defn min->ms [min] (* (* min 60) 1000) then (defn min->ms [min] (-> min (* 60) (* 1000))) then realized it’s just (defn min->ms [min] (* min 60 1000)).

honestly i would absolutely hate to work in a language without parens. text editing is so convenient with them. i think a paren beginner is equivalent to a vim master

once you have something like paredit as muscle memory it seems like you really have lifted off

I am so lost in all editors that don’t sanely add parens lately

cursive spoiled me

i want to brush up on my paren editing skills… does anyone have a link to a good tutorial/docs? I’m using doom emacs atm and smart-parens is mildly annoying at times… i think i had a better paredit setup years ago.

i use lispy and there is a file in the package that is like vimtutor https://github.com/abo-abo/lispy/blob/master/lispytutor/lispytutor.el

there might be something better out there though. Not sure if lispy is the best solution for clojure so would be interested in people's thoughts on that

Personally I’ve been using parinfer which I really love. The code practically writes itself!

nice i’ll read up on those two.

In an attempt to understand datafy/nav a bit further (especially nav), I put together a very simple repo with an example here https://github.com/markbastian/datafy-playground/. The only example of significance is here: https://github.com/markbastian/datafy-playground/blob/master/src/datafy_playground/datafy_file.clj. I was wondering if some of the experts could weigh in on some questions I've had regarding these functions. Here are my questions: 1. Is it appropriate or normal to auto-datafy as you nav? In my example, if I nav from a datafied file to its parent, is there any reason to not just datafy it on the fly? 2. If a datafied item has a nested datafiable entity (in this case a datafied directory has a list of files) is it considered best practice to use collection functions to get at the item and then datafy it (e.g.

(datafy (get-in datafied-directory [:files 2]))

(nav datafied-directory :files 2)

(nav datafied-file :contents :csv)

Hello guys, how would you make a function run one at a time, even if it is called multiple times? I have a compojure route which makes a reservation, but first it checks if there is free-space. So this is a concurrency problem, how would you solve it?

if you use an agent, they enforce a queue on all sends

@markbastian I don't know if this helps answer those questions, but the way I think about it is that you have some Thing (which is an arbitrary object -- Clojure or Java, whatever) and you explicitly call datafy on it to get a pure Clojure data representation of that Thing. Then you can navigate that as a pure Clojure data structure using regular Clojure functions and when you want to go back to the corresponding arbitrary Thing or sub-Thing you call nav, mimicking the pure Clojure data structure navigation. Now you're back in Thing-land, and you would explicitly call datafy again to get to a pure Clojure data representation of that new Thing/sub-Thing.

In the case of REBL, it takes a Thing and calls datafy to get the data it displays in the view pane and when you "drill down", it calls nav to navigate into the Thing, and then calls datafy to get new data to display in the view pane.

@paul931224 alternatively, compare-and-set! or swap! with a function that conditionally aborts

(those functions work on an atom rather than an agent though, so if the source of truth isn't in memory an agent might still make more sense)

if you can model it in an atom as a compare-and-set!, you can do the same in a sql database, and other kinds of databases often have some kind of cas

yeah, letting a db be source of truth for the transaction is smarter

I am a huge fan of a cas, so for a reservation system, cas not-reserved with reserved, and then it doesn't matter how often the function is run

@seancorfield - So, in the cases of a File or a DB thing (a row in a resultset, for example), datafy takes you from File or Row to Clojure data (likely a map). This part makes sense to me. WRT nav, are you saying nav on a map would take me back to a File, Row, or other Thing-type corresponding to where you are navigating?

@noisesmith the problem is the source is mongodb. Read and writes can't be atomic together, I just want to put functions in queque like in core.async, but I want to wait still one ends before the other starts

agents have this behavior, but it's going to be fragile

eg. what if two servers are running your app?

@paul931224 You may need to consider here, what is going to happen if you ever load balance over more than one server 🙂.

with no distributed reliable source of truth, bad things will happen

Or once you are in data-land do you capture the scope of the original thing (e.g. the FileSystem or DB) and just work in data?

you will need to stand up something like zookeeper or etcd to get cas on top of a non-transactional store

yeah, a dedicated reliable source of truth is an option

(or implement a consensus algorithm yourself, which has hazards)

@wesley.hall I am way too amateur too consider this yet. This is my third full-stack application till now, and this one have real clients, so this is my first concurrency problem 😄

or a db that provides this while also storing your data - such things exist

using a queue doesn't really enforce what you want

well I just want to block other operations while I read, calculate then update the new value

so a queque with blocking 😄

a queue with blocking doesn't

@paul931224 Well, here's an interesting option. If you choose to represent each "ticket" in your mongo database as an individual document, you should be able to use the mongo function, "findOneAndUpdate()", to find a "free ticket" and reserve it.

Then you can load balance later if you need to 🙂

the best thing to do is likely just not use mongo

@wesley.hall well this is a bit more complex, I store free-times in minute intervals [[600 1000][1200 1440]]... so I can't update with mongo logic, I need my clojure power to make new ranges of minutes etc.

my all reservation logic is about ranges, remove ranges from ranges, then keep the new ranges

@paul931224 Honestly, you might need to rethink that if you want a robust solution to this problem. It's not uncommon to have to do this, particularly with something like mongo. You often have to design your data storage around operational requirements.

You could also look at java.util.concurrent if nothing obvious to be found in clojure. Lots of "locky" type stuff in there, but locking your entire system while one person makes a booking strikes me as a... non-ideal solution.

Incidentally, many large systems solve this problem by just "overselling" and solving the problem later 🙂.

I want to lock only the function. only adding reservation and modifying it, is a problem, which happens like 40 times a day, the problem is it happened at the same time once, so reservation overlapped each other.

Moved to separate thread...

well, I thought it wont be a problem for a time myself

but in first week it happened 2 times 😄

it is like 2 guys picking same date, same hour, at same guy, in the same 5 ms-es

well, anyway, I need an easy fix, because I can't make a new architecture in one night. For example storing a state in atom, setting it to true if running, false after the update, and the function should recur still it is false, so it can run and set it true and etc...

@markbastian I answered in a thread to avoid cluttering the main channel.

@paul931224 Maybe look at (locking), you can just def some kind of object in the namespace and lock on it. I am not sure I would advise this as an actual long term solution, but it will probably do what you need for now.

btw my first suggestion, using an agent, is effectively a queue plus locking plus execution on a separate thread

Yeah, or use an agent 🙂

looking in both, your help is much appreaciated 🙂

locking might be better, making things async via threads might just increase complexity here

Yeah, in retrospect, not even sure how you do this with an agent, more asynchronity there, not less. Though in fairness I don't use them much, so might be missing something.

you send the reservation setting function to the data defining reservations

the setting functions are guaranteed to not run concurrently

Really? Then why do they run in a thread pool?

I guess I really don't understand these things.

they run async from the caller, but no two agent functions on the same agent overlap

as far as the agent itself is concerned, zero concurrency

Oh, I see.

so agents are perfect for a case where you need a single source of truth, no retries, no overlapping changes as long as it's OK for all of this to be async from the perspective of the code doing the modification

So, tricky to know if reservation has gone through I guess.

well my customer will mention it for sure 😄

Haha

Well, that does seem to be the airline model. Over sell and kick the can down the road to the poor customer service person at the airport.

There's always that approach 😉

yeah, a given agent will wait for the result of its last execution before starting its next.

Definitely took me a while to re-grok that fact. References to, "thread pools" in the (send) docs are actually misleading because it does suggest that sends are done concurrently, but what is really meant here is that there is a single thread pool that is shared across all agents for (send). I think I did know this once... but honestly, how often do you use this stuff? 🙂